Optical Die-Down Quad Flat Non-Leaded Package

ABSTRACT

An optical sensor package that includes an optical sensor die is mounted by flip chip interconnect onto a lead frame in a “die-down” orientation, that is, with the active side of the optical sensor die facing the lead frame. An opening is provided in the lead frame die paddle (pad), and light passes from outside the package through the opening in the lead frame die pad onto light collection elements on the active side of the chip.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.60/677,994, titled “Optical die down quad flat non-leaded package”,filed May 5, 2005, which is hereby incorporated by reference herein.

BACKGROUND

This invention relates to image sensors and, particularly, tosingle-chip image sensor packaging.

The semiconductor sensor die employed in many digital cameras are wirebonded to the substrate or leadframe, so the die is oriented active faceupward (in relation to the substrate or leadframe), with an opening toadmit light in the molding overhead, or with a clear molding compound ora glass window in the molding overhead.

SUMMARY

Generally, the invention features an optical sensor package thatincludes an optical sensor die mounted by flip chip interconnect onto alead frame in a “die-down” orientation, that is, with the active side ofthe optical sensor die facing the lead frame. An opening is provided inthe lead frame die paddle (pad), and light passes from outside thepackage through the opening in the lead frame die pad onto lightcollection elements on the active side of the chip.

In one general aspect, the invention features an optical sensorsemiconductor chip package, including: a lead frame having first andsecond sides and including a paddle and peripheral leads, and a diehaving an active side including a sensor area having an array ofphotosensor elements, and peripheral interconnect sites. The die ismounted onto the lead frame by flip chip interconnection; that is, theactive side of the die faces the second side of the lead frame, andinterconnect sites on the active side of the die are electricallyconnected to corresponding bond fingers on the second side of the leadsby balls or bumps. An opening through the die paddle is situated suchthat the opening in the paddle and the sensor area are at least partlyaligned. The opening in the paddle defines a paddle margin, and a sealis provided between the second side of the paddle margin and the activeside of the die. The package is encapsulated, and the seal prevents theencapsulant from contaminating the sensor area of the die.

In some embodiments the die includes a charge coupled device (CCD) imagesensor; in other embodiments the die includes a complementary metaloxide semiconductor (CMOS) image sensor. The image sensor can provideeither a digital or an analog output. The image sensor can be either acolor image sensor or a monochrome image sensor.

In some embodiments the interconnect employs a gold stud bump; in otherembodiments the interconnect employs a solder bump.

In some embodiments the sensor area of the die is covered with alight-transmitting material. The light-transmitting material maytransmit nearly all or only a part of light directed toward the die; forexample, it may reduce the intensity of transmitted light in all or aportion of the spectrum, and it may specifically reduce the intensity oftransmitted light in one or more selected portions of the spectrum. Insome embodiments the opening through the paddle may be covered with alight-transmitting material, as a window.

In another general aspect the invention features a device including theoptical sensor package; such devices include, for example, opticalpointing devices (such as so-called “optical mouse”), cameras (such asso-called “web cam”), digital cameras (including video cameras and stillcameras), and cameras that constitute part of a portabletelecommunications device (camera in a mobile telephone for example),and the like.

In another general aspect the invention features a method for making anoptical sensor semiconductor package.

The optical sensor package according to the invention has a thinnerprofile, owing to the flip-chip interconnection, with the active(sensing) side of the die facing the leadframe. A typical flip chipinterconnect bump height, die-to-leadframe, is ˜70 um. Where a lens isdesired, the lens can be attached directly to the die pad, so theoverall package thickness is less than for a die-up wire bond, wherewire loop height and molding thickness contribute to package thickness.Also, the optical package according to the invention can be madeinexpensively—less than for an equivalently functioning wire bondedoptical package—because there are fewer assembly steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view, partly from a photomicrograph and partlysketched, showing a quad flat non-leaded package.

FIG. 2 is a diagrammatic partially cut away perspective view of a quadflat non-leaded package as in FIG. 1.

FIG. 3A is a sketch in a plan view showing the lead frame side of apackage according to an embodiment of the invention.

FIG. 3B is a sketch of a package as in FIG. 3A, in a sectional view thruB-B.

FIG. 3C is a sketch in an elevational view of a package as in FIG. 3A.

FIG. 3D is a diagrammatic partially cut away perspective view of apackage according to the invention, as in FIG. 3A.

FIG. 4A is a sketch in a plan view showing the lead frame side of apackage according to an embodiment of the invention.

FIG. 4B is a sketch of a package as in FIG. 4A, in a sectional view thruB-B.

FIG. 5A is a sketch in a plan view showing the lead frame side of apackage according to an embodiment of the invention.

FIG. 5B is a sketch of a package as in FIG. 5A, in a sectional view thruB-B.

DETAILED DESCRIPTION

The invention will now be described in further detail by reference tothe drawings, which illustrate alternative embodiments of the invention.The drawings are diagrammatic, showing features of the invention andtheir relation to other features and structures, and are not made toscale. For improved clarity of presentation, in the FIGS. illustratingembodiments of the invention, elements corresponding to elements shownin other drawings are not all particularly renumbered, although they areall readily identifiable in all the FIGS.

The package can suitably be constructed as a die-down quad flatnon-leaded package in which an opening is provided in the die pad of thelead frame, providing for passage of light from outside the package ontothe active surface of the die. A seal is provided between the margin ofthe paddle, around the opening, to prevent encapsulant fromcontaminating the optical sensor area of the die.

Turning now to FIGS. 1 and 2, there is shown a flip chip quad flatnon-leaded package (“FC-QFN” package). The FC-QFN package includes alead frame including a die pad 13 and leads 12, and a die 14 mounted ona die attach side of the lead frame by flip-chip interconnect 15. Thelead frame may be made of copper, by for example masking and etching acopper sheet. The die, the interconnects and at least the die attachside of the lead frame are enclosed in an encapsulant 17. The QFNpackage is referred to as “non-leaded”, because, rather than havingextensions of the lead 12 beyond the encapsulation 17 for electricalconnection of the package to, for example, a motherboard, connection ofthe QFN package is made by way of exposed portions 16 of the leads 12.The exposed portions 16 are substantially flush with the encapsulant onthe leadframe side of the package. FC-QFN packages can be made highlycompact (thin, with a small footprint in relation to the die size). Atypical FC-QFN package may have a 5 mm×5 mm footprint, for a 3 mm×3 mmdie. The package is thin, owing to the low profile of the flip-chipinterconnect, which may include, for example, a gold bump on the dieconnected to a high-Pb bump on the leadframe.

According to the invention, an optical sensor is constructed using a QFNpackage substrate in which an opening has been provided in the die padfor passage of illumination onto the active side of the die. Referringnow to FIGS. 3A, 3B, 3C and 3D, there is shown an embodiment of anoptical sensor package according to the invention. The die 34 is mountedon the leads 32 by flip chip interconnection 35. An opening 31 (herecircular) in the die pad 33 permits light to pass from outside thepackage onto the active side 39 of the die 34. A barrier 381 which maybe an adhesive material, is compressed between the die pad 33 and theactive side 39 of the die 34 to prevent flow of the encapsulant 37 ontothe sensor portion of the active side of the die. The barrier may havethe form of a ring, as shown by way of example by broken lines 38 inFIG. 3D or a rectangle (e.g., square), for example. Exposed surfaces 36of the leads 32 provide for electrical connection of the package with,for example, a motherboard or other circuitry in the device in which thepackage is employed. An array of such packages are typically formed,beginning with a lead frame array, and then saw singulated followingencapsulation to form individual packages. In conventional QFNprocessing, a coverlay is provided during processing on the side of theleadframe opposite the die attach side; typically the coverlay isremoved following encapsulation. Here, the coverlay may be left in placeto protect the active side of the die from contamination duringprocessing, until the final test of the functionality of the sensorpackage.

The optical sensor package according to the invention may be made verythin, providing for a very short light path. Overall package thicknessabout 0.7 mm can be readily obtained, and reduction of thickness to 0.5mm or less is possible.

Embodiments as in FIGS. 3A-3D can be useful particularly in low endapplications such as an optical pointing device (“optical mouse”, e.g.)or an optical data scanner or reader such as a DVD reader, in whichimaging quality may acceptably be low. Alternatively, the active side ofthe die may be protected by a coating, as shown in FIGS. 5A, 5B; or, thedie pad may be half-etched to provide a step in which a glass or plasticinsert may be placed to protect the die from contamination and, furtherto provide some optical function, as described with reference to FIGS.4B, 4C.

Referring now to FIGS. 4A and 4B, generally as in FIGS. 3A-3B, the die34 is mounted on the leads 42 by flip chip interconnection 45. Anopening (here circular) in the die pad 43 permits light to pass fromoutside the package onto the active side 49 of the die 34. A barrier 44,which may be an adhesive material, is compressed between the die pad 43and the active side 49 of the die 34 to prevent flow of the encapsulant47 onto the sensor portion of the active side of the die. The barriermay have the form of a ring or a rectangle (e.g., square), for example.Exposed surfaces 46 of the leads 42 provide for electrical connection ofthe package with, for example, a motherboard or other circuitry in thedevice in which the package is employed. In this embodiment, a portionof the die pad 43 adjacent the opening is half-etched to provide a step,in which a transparent cover 41 may be mounted and affixed using asealant or adhesive 48. The cover may be, for example, made of glass orof plastic; and it may be translucent to a broad portion of theelectromagnetic spectrum (such as, for example, the visible spectrum),or to selected portion(s) of the spectrum, depending upon the particularapplication. According to the particular application, the cover may bedesigned to provide little or no optical imaging effect; or, it may beshaped as a lens. And, according to the application, the material of thecover may be selected to provide substantially no filtration of theentering illumination or, alternatively, to provide selected broad-bandor selected narrow-band filtration.

The cover may be applied either following singulation of the packages,or—to protect the die during processing—following singulation.

Embodiments as in FIGS. 4A and 4B can be useful particularly inapplications where higher quality imaging is required, as for example incell phone cameras (employing CCD or CMOS imaging technology).

Referring now to FIGS. 5A, 5B, a coating 68 may be provided over theactive (sensor) side 59 of the die 34. The coating may be applieddirectly onto the die surface. Generally as in FIGS. 3A-3B, the die 34is mounted on the leads 52 by flip chip interconnection 55. An opening(here circular) in the die pad 53 permits light to pass from outside thepackage onto the active side 59 of the die 34. A barrier 54, which maybe an adhesive material, is compressed between the die pad 53 and theactive side 59 of the die 34 to prevent flow of the encapsulant 57 ontothe sensor portion of the active side of the die. The barrier may havethe form of a ring or a rectangle (e.g., square), for example. Exposedsurfaces 56 of the leads 52 provide for electrical connection of thepackage with, for example, a motherboard or other circuitry in thedevice in which the package is employed. The material of the coating maybe selected according to the function of the sensor and its sensitivity,and may be selected to provide provide substantially no filtration ofthe entering illumination or, alternatively, to provide selectedbroad-band or selected narrow-band filtration.

Embodiments as in FIGS. 5A and 5B can be useful particularly in low endaplications such as an optical pointing device (“optical mouse”, e.g.)or an optical data scanner or reader such as a DVD reader, or in aso-called “web cam”, in which imaging quality may acceptably be low.

Other embodiments are within the scope of the invention.

1. An optical sensor package comprising an optical sensor die mounted byflip chip interconnect onto a lead frame in a “die-down” orientation. 2.The optical sensor package of claim 1 wherein the lead frame comprises adie paddle and peripheral leads, and wherein an opening through the diepaddle is at least partly aligned with a photosensitive area on the die.3. An optical semiconductor chip package, comprising a lead frame havingfirst and second sides and comprising a paddle and peripheral leads, theleads comprising bond fingers; and a die having an active side includinga sensor area comprising an array of photosensor elements and peripheralinterconnect sites; wherein the die is mounted onto the lead frame byflip chip interconnection at sites on leads at the second side of theleadframe, and an opening through the die paddle is situated such thatthe opening in the paddle is at least partly aligned with the sensorarea.
 4. The optical semiconductor chip package of claim 3 wherein theopening in the paddle defines a paddle margin, and further comprising aseal surrounding the margin between the second side of the paddle andthe active side of the die.
 5. The optical semiconductor chip package ofclaim 4 wherein the package is encapsulated.
 6. The opticalsemiconductor chip package of claim 3 wherein the die comprises a chargecoupled device image sensor.
 7. The optical semiconductor chip packageof claim 3 wherein the die comprises a complementary metal oxidesemiconductor image sensor.
 8. The optical semiconductor chip package ofclaim 3 wherein an image sensor on the die provides a digital output. 9.The optical semiconductor chip package of claim 3 wherein an imagesensor on the die provides an analog output.
 10. The opticalsemiconductor chip package of claim 3 wherein an image sensor on the dieis a monochrome image sensor.
 11. The optical semiconductor chip packageof claim 3 wherein an image sensor on the die is a color image sensor.12. The optical semiconductor chip package of claim 3 wherein the flipchip interconnection comprises a solder bump.
 13. The opticalsemiconductor chip package of claim 3 wherein the flip chipinterconnection comprises a gold stud bump.
 14. The opticalsemiconductor chip package of claim 3 wherein the sensor area of the dieis covered with a light-transmitting material.
 15. The opticalsemiconductor chip package of claim 14 wherein the light-transmittingmaterial reduces the intensity of transmitted light over a broadspectral range.
 16. The optical semiconductor chip package of claim 14wherein the light-transmitting material reduces the intensity oftransmitted light over a portion of the spectral range.
 17. The opticalsemiconductor chip package of claim 14 wherein the light-transmittingmaterial reduces the intensity of transmitted light over at least onespecified portion of the spectral range.
 18. The optical semiconductorchip package of claim 3 wherein the opening through the paddle iscovered with a light-transmitting material.
 19. The opticalsemiconductor chip package of claim 18 wherein the light-transmittingmaterial comprises a window.
 20. The optical semiconductor chip packageof claim 18 wherein the light-transmitting material comprises a lens.21. The optical semiconductor chip package of claim 18 wherein thelight-transmitting material comprises an image-forming lens.
 22. Adevice comprising the optical semiconductor chip package of claim 3,connected to circuitry in the device.
 23. An optical pointing devicecomprising the optical semiconductor chip package of claim 3, connectedto circuitry in the device.
 24. A camera comprising the opticalsemiconductor chip package of claim 3, connected to circuitry in thecamera.
 25. A portable telecommunications device comprising the opticalsemiconductor chip package of claim 3, connected to circuitry in thedevice.
 26. A method for making an optical semiconductor chip package,comprising: providing a lead frame having first and second sides andcomprising a paddle and peripheral leads, the paddle having an openingtherethrough and the leads comprising bond fingers; providing a diehaving an active side including a sensor area comprising an array ofphotosensor elements and peripheral interconnect sites; aligning the diewith the die paddle so that the sensor area on the die is at least partyaligned with the paddle opening; and mounting the die onto the leadframe by flip chip interconnection at sites on leads at the second sideof the leadframe.
 27. The method of claim 26, further comprisingproviding a seal material on the second side of the die paddle,surrounding the opening, wherein aligning the die with the die paddlecomprises contacting the die with the seal material.
 28. The method ofclaim 27, further comprising, following the die mounting step,introducing an encapsulant between the die and the leadframeperipherally to the seal material.